This project focuses on the role of signal transduction mechanisms in hippocampal neuronal plasticity and memory formation. In the most recent Project Period we have been exploring the role of the TET Dioxygenase family of signal transduction cascades in hippocampal neuronal plasticity and learning, focusing on the mechanisms through which this pathway controls memory-associated gene transcription. We initiated our studies in this area about 10 years ago by determining that epigenetic mechanisms including histone acetylation and DNA Methyltransferase activity are necessary for NMDA receptor-dependent LTP in area CA1. We then transitioned to studies in the behaving animal and discovered that epigenetic mechanisms are activated in the hippocampus with contextual associative conditioning, and that alterations in epigenetic mechanisms are necessary for fear conditioning and for spatial learning. Studies from a wide variety of laboratories have now shown that epigenetic signaling is involved in many forms of synaptic plasticity and learning, in essentially every species that has so far been examined including humans. Moreover, in the last Project Period, we as well as the Tsai lab discovered that TET1 Oxygenase is a controller of active DNA demethylation in the CNS, and that this pathway regulates memory capacity in the behaving animal. Given the clear importance of understanding the roles and regulation of TET Oxygenase-dependent epigenetic mechanisms in neural plasticity and learning, for the next Project Period we propose to continue our investigations into the genomic, epigenomic, and functional targets of TET Oxygenase regulation in the hippocampus. We will pursue the following three Specific Aims: 1: To test the hypothesis that TET1 drives active demethylation at memory-associated genes. 2: To test the prediction that site-specific gene demethylation is sufficient to alter gene expression and regulate memory formation. 3: To test the specific hypothesis that TET1 regulates memory capacity via controlling homeostatic synaptic plasticity and cell-wide excitability in hippocampal pyramidal neurons. By focusing on these important new targets for the TET Oxygenase pathway in hippocampus, we will continue to formulate a comprehensive model of epigenetic regulation of transcription-dependent molecular mechanisms in neuronal plasticity and memory.